The newspapers frequently give news of the rate of exchange between different currencies, e.g. 1 USD = 60.21 INR, which means that you have to give 44.56 INR to buy 1 USD. This would be middle rate. It is between the rate at which banks are selling USD dollars in exchange for INR and the rate which banks are buying USD dollars for INR.
Middle rate gives a rough indication to the public of how many INR are required to buy 1 USD.